Would Ten Hag want that job?
I think Potter would. It's a step up in prestige, and there are some parts he could work with. I think Ten Hag could have a better job than Spurs (who will be without CL / Europa, losing their best player is likely), and I think they're a rebuild more than a reshuffle and get back in the mix.
There is no doubt that Spurs are in a bit of a "rot" right now, but they are still among the top 10 richest clubs in the world, plays in the PL, based on London, got a fantastic stadium and world class training facility. You only got so many shots at a job like that - regardless of how 21/22 looks.
Not sure if selling Kane would be a discouragement at all. Why wouldn't a new manager want 200m to shape his own team with? I think the Spurs job would be less attractive if you are being told Kane stays, but you got to go along with players like Dier, Sanchez, Aurier, Doherty, Reguilon etc. being your defense.
Not to say that I think it is a given ten Hag would move to Spurs if he got offered the job. So many things that might influence someone's decision making on these kind of things. Might even be having kids that would rather finish school in one country, a special connection at Ajax or as you say first thinking Ajax will be more interesting in 21/22 than Spurs - while he might also think maybe a bigger team like Spurs would be a possibility if he does well with Ajax again. However, I do believe, without knowing much about his personality, that he would join if Spurs pushed hard for him. That is also the thing with these kind of things. A manager would like to know (or get the feeling) that he is the main man. Leaving Ajax to get sacked after 27 games would obviously be a waste.
I see Pochettino getting more and more popular among the bookmakers. He has suddenly become the big favourite for the job. I wanted him gone when he left, but I wouldn't mind him coming back. Maybe a bit early though - I was thinking 5-10 years down the line.